The present invention relates to a structure of a cylindrical boss forming place of a cabinet.
Various electric devices such as a television receiver and a DVD player comprise a cabinet for accommodating electric components therein. Such a cabinet may be made of resin and formed by an injection molding. A resin molded cylindrical boss may be integrally formed on a back surface of an outer plate of the cabinet. When such a cylindrical boss is integrally formed on the back surface of the outer plate of the cabinet, a “sink” may be generated on a front surface of the outer plate due to the contraction of resin during the molding process. If the sink is generated on the outer plate, especially on the front surface of the outer plate of a front panel, during the molding process, it noticeably deteriorates an external appearance quality, such as premium looking, of the device. Consequently, there have been various measures to prevent the sink from occurring on the surface of the cabinet or to make the sink unnoticeable (see Patent Document 1).
FIG. 4 is an explanatory diagram illustrating a resin molded product including a base plate 1 with a flat front surface and a rib 2 standing on a back surface of the base plate. Generally, in this resin molded product, if the relationship of the following formula (1) is satisfied, a sink does not occur on the front surface of the base plate:a<A×0.6  (1)where “A” denotes a thickness of the base plate 1 and “a” denotes a thickness of the rib 2. This is due to the fact that, under the condition that the relationship of the formula (1) is satisfied, since the cooling speed of the resin in the connecting portion of a base end (a root) of the rib 2 and the base plate 1 is similar to the cooling speed of the resin in the surrounding portion disposed around the connecting portion during the injection molding process, local temperature contraction of the resin hardly occurs. Further, FIG. 4 shows a place where the sink easily occurs and the shape of the sink with dotted lines H, as an example.
Moreover, in the patent document 1, it is described that, in the relationship between the thickness t of a surface with a thickness deviation portion and the width w of the thickness deviation portion on a mold for forming the thickness deviation portion, when an injection molded product satisfying w>0.6 t is molded, the sink is likely to occur.
In the cabinet of the electric device such as a television receiver, the front panel is made to be thin so as to promote weight or cost reduction. On the other hand, a cylindrical boss is integrally formed on the back surface of the outer plate of the thin front panel by the injection molding to reinforce the outer plate by the cylindrical boss. The cylindrical boss is used for fixing the CRT and a liquid crystal module in the cabinet with screws. In the cabinet in which the cylindrical boss is integrally formed on the back surface of the outer plate, depending on the thickness of the outer plate and the thickness of the cylinder wall of the base end of the cylindrical boss, the sink may occur on the front surface of the outer plate, thereby deteriorating the external appearance quality. Particularly, in a cabinet with a high gloss, the sink generated on the outer plate is likely to be noticeable.    Patent Document 1: JP-A-10-151640
In order to prevent the sink from occurring, the thickness of the outer plate and the thickness of the cylinder wall of the base end of the cylindrical boss may be set to satisfy the condition of the formula (1). However, in view of requisition of thin outer plate and required strength of the cylindrical boss, the condition of the formula (1) may not be easily satisfied.
Meanwhile, although the measures to suppress the occurrence of the sink have been performed, mainly, by the mold manufacturer, it is difficult to suppress or prevent the occurrence of the sink on the front surface of the outer plate only by means of the measures of the mold manufacturer.